The fused shader stored black with alpha 1 for a pixel whose source
coordinate left the frame, and the merge's warp averaged it in like any
other: a dark, badly interpolated fringe along every frame's edge, visible
as a seam wherever a frame ended and, later, as the edge the border fill
continued. The display keeps its opaque black; CameraLinear stores alpha 0
and the warp weights each sample by the alpha it interpolated, dropping a
sample that has none.
dtourolle
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